A diode, which is a rectifying device connected between two external terminals, operates such that when a voltage is applied in a forward direction, the diode allows a current to flow in one direction from the anode side to the cathode side, and when a reverse voltage is applied, the diode blocks a current in a reverse direction from flowing. Such a general diode is used for a redundant power supply, rectifier or the like. However, in such a diode, a forward voltage occurs during conduction, and a relatively large conduction loss occurs in accordance with a product of this voltage and a forward current. In particular, in the case where a plurality of serially connected diodes are used in a redundant system or the like, there is a problem that the loss increases by the number of connected diodes.
A low power consumption diode circuit, which is a conventional rectifier with low conduction loss, has an anode wire and a cathode wire, and includes a comparator, a switch and a diode. The comparator has two inputs, and the anode wire is connected to one of the inputs, and the cathode wire is connected to the other input. When a voltage of the anode wire is greater than a voltage of the cathode wire by more than a predetermined forward voltage, the comparator outputs a high logic level signal to an output line, and the switch switches so as to allow conduction, whereby the anode wire and the cathode wire are electronically connected (e.g., Patent Document 1).
A two-terminal synchronous rectifier, which is another example of a conventional rectifier with low conduction loss, includes: a field-effect transistor having its source-drain path in a first arm between the two rectifier terminals; a gate-control circuit, connected to the gate electrode of the transistor, for turning on/off the transistor synchronously in accordance with voltage reversal at the two rectifier terminals; and further, a parallel arm including a charge pump formed thereon, which charge pump is driven by a voltage difference between the two rectifier terminals so as to drive the gate-control circuit. Also, a pn diode is intrinsically formed within the transistor (see, e.g., Patent Document 2).
[Patent Document 1] Japanese Laid-Open Patent Publication No. H07-297699
[Patent Document 2] Japanese National Phase PCT Laid-Open Publication No. 2004-519991